GCN Circulars
GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.
Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search
To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.
Advanced Search Examples (click to copy):
subject:"Swift"body:"GRB"submitter:"Judith Racusin"26037 results found.
- GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
- GRB 250911A: Enhanced Swift-XRT position
- GRB 250911A: Swift-XRT observations
- GRB 250911A: COLIBRÍ optical counterpart candidate
- GRB 250911A: Swift detection of a burst
- GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
- GRB 250910A: SVOM/MXT possible afterglow detection
- GRB 250702B: Late time Chandra observations
- EP250908b/EP#01709240653: Swift/UVOT Detection
- EP#01709240653: Swift-XRT observations
- EP250908c: VLT/FORS2 optical counterpart identification
- GRB 250905A: Swift-BAT refined analysis
- GRB 250903A: Swift-XRT afterglow detection
- GRB 250905A: Swift-XRT refined Analysis
- GRB 250904A: Swift-BAT refined analysis
- GRB 250905A: Swift/UVOT Upper Limits
- GRB250904A: Liverpool Telescope upper limits
- GRB 250905A: Enhanced Swift-XRT position
- GRB 250904A: Swift/UVOT Detection
- GRB 250903A: Swift/UVOT detection
- GRB 250904A: Swift-XRT refined Analysis
- GRB 250905A: KAIT optical upper limit
- GRB 250905A: Swift detection of a burst
- Swift GRB250905.09: Global MASTER-Net observations report
- Swift GRB 250904A: Global MASTER-Net observations report
- GRB 250904A: Enhanced Swift-XRT position
- GRB 250904A: TRT optical counterpart detection
- GRB 250904A: Prompt enhanced Swift-XRT position
- GRB 250904A: Swift detection of a burst
- GRB 250903A: Swift-XRT observations
- EP250903a: Swift-XRT observations
- EP#01709201209: Swift-XRT observations
- EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
- GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
- GRB 250903A: LCO optical observation
- GRB 250903A: LCO optical afterglow detection
- EP250901a: Mondy, Assy and SAO RAS optical limits
- Subject GRB 250903A: SVOM/MXT afterglow detection
- EP250903a: LCO candidate counterpart discovery
- GRB 250901A: Swift/UVOT Upper Limit
- GRB 250830B: Swift-XRT afterglow detection
- GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
- GRB 250901A: EP-FXT follow-up observation
- GRB 250901A: NOT optical observations
- GRB 250901A: SVOM/VT optical afterglow with VHF data
- GRB 250901A: Swift-XRT afterglow detection
- EP250901a: Swift-XRT observations
- GRB 250901A: LCO optical upper limit
- EP250827b: Swift observations of AT 2025wkm
- EP250831a: NOT optical observations and tentative afterglow candidate
- GRB 250901A: SVOM detection of a burst
- EP250831a: EP-FXT follow-up observation
- EP250831a: Swift-XRT observations
- GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
- GRB 250831A: Swift-XRT counterpart detection
- GRB 250830B: Swift-XRT observations
- EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
- GRB 250830B: Swift ToO observations
- GRB 250830B: MAXI/GSC detection
- GRB 250828B: Swift-BAT refined analysis
- EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
- Swift GRB 250828B: Global MASTER-Net observations report
- EP250828a: KAIT optical upper limit
- EP250827a: Swift/UVOT Detection
- GRB 250828B: Swift detection of a burst
- EP250827a: STEP/T80S Confirmation of fading optical counterpart
- EP250827a: confirmation of optical rebrightening with LCO
- EP250827a: GOTO observation of the optical afterglow
- EP250827a: Swift-XRT counterpart detection
- GRB 250806A: HiPERCAM/GTC limits on a possible supernova
- GRB 250823A: Swift-BAT refined analysis
- GRB 250823A: Swift-XRT refined Analysis
- LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
- GRB 250823A: COLIBRÍ optical observations
- GRB 250823A: SVOM/VT optical observation
- GRB 250823A: Swift/UVOT Detection
- GRB 250823A: NOT optical observations
- GRB 250823A: Fermi GBM Observation
- GRB 250818B: MeerKAT Detection
- GRB 250823A: Enhanced Swift-XRT position
- GRB 250823A: LCOGT Optical Detection
- GRB 250823A: BOOTES6/DPRT early optical detection
- GRB 250823A: Liverpool Telescope optical detection
- GRB 250823A: Swift detection of a burst
- Swift GRB250823.84: Global MASTER-Net observations report
- GRB 250821A: Kilonova-Catcher optical upper limits
- EP250821a: Swift/XRT counterpart fading
- GRB 250821A: Swift-BAT refined analysis
- EP250821a: Swift/UVOT further observations.
- GRB 250821A: VLT/FORS2 Optical Observation
- GRB 250821A: GECAM-B detection
- EP250821a: SVOM/VT optical observation
- GRB 250821A: NOT z-band upper limit
- GRB 250821A: KAIT optical upper limit
- GRB 250821A: Swift-XRT refined Analysis
- Swift GRB 250821A: Global MASTER-Net observations report
- GRB 250821A: Enhanced Swift-XRT position
- GRB 250821A: Swift/UVOT Upper Limits
- EP250821a: Rapidly fading optical source detected in Las Cumbres followup
- EP250821a: Swift XRT and UVOT counterpart detection